Plastic internal rocket nozzle



Sept. 17, l1963 R. F. VETTER ETAL PLASTIC INTERNAL ROCKET NozzLE Filed Nov. l5, 1960 INVENTORS. RONALD F. VETTER RAY A. MILLER STEPHEN H. HERZOG BY fA/Lmbf ATTORNEY.

United States Patent Oli ice Patented Sept. 17, 1963 3,103,784 PLASTIC INTERNAL RUCKET NOZZLE Ronald F. Vetter, Ray A. Miller, and Stephen H. Herzog,

China Lake, Calif., assig-'nors to the United States of America as represented by the Secretary of the Navy Filed Nov. 15, 1960, Ser. No. 69,529 6 Claims. (Cl. titl-35.6) (Granted under Title 35, U.S. Code (1952), sec. 266) The invention described herein may be manufactured tand used by or for the Government of the United States of America for governmental purposes without the payment of any royalties thereon or therefor.

The present invention relates generally to improvements in internal rocket nozzles yand more particularly to a new and improved plastic internal rocket nozzle for a composite propellant system which may be bonded directly'to ya composite propellant grain, the structure of which reduces or practically eliminates thermal stress to the nozzle closure.

In the field Aof rocketry it has been the practice to fabricate internal nozzles of graphite and metal which could not be bonded directly to the cast composite propellant grain because of the high heat transfer rate through the graphite and metal. The graphite and steel internal nozzles are sometimes very fragile yand must be handled with extreme care; furthermore, the fabrication of the :graphite and steel nozzles is la long and costly process. 'Although these nozzles have served the purpose, 'they have not proved entirely satisfactory under all conditions of service `for the reasons that considerable diilicultyhas been experiencedat high temperatures requiiing elaborate -gas'sealing systems `and special precautions must be taken to insure that the rocket engine can withstand the high temperature iand quantity of heat transferred without malfunction. g The general purpose of this invention is to provide an internal plastic nozzle for composite propellant systems which embraces all the advantages of similarly employed rocket nozzles and possesses none of the aforedescnibed disadvantages. To Iattain this, the present invention contemplates `an internal nozzle comprising a beat-resistant resin molded under extreme pressure and temperatures to which nozzle inserts made of graphite `or other suit- !able material are attached wherebyv the compositepropellant grain is bonded directly to the nozzle thereby giving higher motor-loading density and increasing resistance to mechanical shock.

An object .of the present invention is to provide la plastic nozzle which permits the composite propellant |grain to be bonded directly to the rocket nozzle.

Another object is to provide fan internal rocket nozzle structure which is light in weight.

A further object of the invention is the provision of .an internal rocket nozzle structure which is resistant -to thermal shock and eliminates or greatly reduces the thermal load on the nozzle closure.

Still another object is to provide a plastic internal rocket nozzle which can be mass fabricated simply and cheaply.

Other objects and features of this invention will become apparent to those skilled in the lar-t as the disclosure is made in the following detailed description when considered in connection with the .accompanying drawing in which like reference numerals designate like parts throughout .the figures thereof.

In the accompanying drawing which illustrates [an em-l bodiment of the present invention, the single FIGURE is a partial longitudinal section through the rocket moto-r casing ,and associated parts thereof disclosing the nozzle end of the motor in which la composite propellant :grain is cast in place.

Referring more particularly to the accompanying drawing, the rocket motor structure shown comprises a heatresistant casing or combustion chamber 11, which may be of a generally cylindrical, spherical, or sphericocylindrical cross-section, closed at its forward or head end, designated generally by numeral 13, and fitted at its `aft end with `an internal nozzle designated generally by numeral 15. A composite propellant grain or change 17, is introduced into chamber llthrough the head end Vland `allowed to solidify around a longitudinally extending core (not shown) to form a central perforation 19 which in the embodiment illustrated is multi-star shaped, but may be of any other `suitable cross-section. The composite propellant grain comprises an oxidizer and fuel, with the oxidizer 1an inorganic salt and the fuel au organic plastic, resin, or elastomeric material. A liner 21 of a beatinsulating material, as, for example, asbestos and a suitable resin binder, is molded to follow along the inner surface or contour of chamber or casing .11. An inhibiting material 23, composed of ,a nonburning material applied, generally by spraying, provides la good surface to which the propellant can be bonded. An internal nozzle design-ated generally by numeral `15 is positioned in the `aft end of rocket chamber 11 and comprises a `single-port plastic exit cone 25 the wall of which converges to fonm an area of restricted diameter, .designated as apex surface or section 2.6, the outside walls of the .cone being bonded directly to composite propellant grain 17, and a preformed inlet cone or insert 27 pressed or bonded to surface 26 of cone 25. Insert 27 comprises a hollow inlet cone portion or section designated by numeral 29, a throat portion or section 31 land lan exit cone portion or section 33 having a surface which corresponds to the apex surface 26 of plastic cone 25.

It lis to be noted that lapexsurface 26 of cone 25 is truste-:conical and that the corresponding surface on section 33 of insert 27 is in face-to-face relation and mates therewith. Such a structural arrangement serves two purposes: (1) pressure of the rocket gases lforces the aforesaid surfaces into tighter engagement, thus requiring only ya light bond therebetween, and (2) a greater area of plastic is provided to which the propellant may be bonded, thus increasing loading density.

Exit cone25 was block-molded and machined from a heat-stable thermosetting material, such sas phenolic resinasbestos iiller, 4to form a conical nozzle with a flange or lshoulder 24, which if cut through at any point perpendicular to the nozzle axis, the Vexposed area is circular. These types `of materials are well known to those skilled 4in the art and could be, if desired, of the type disclosed in Ward U.S. Patent No.- 2,835,107, or any like material suitable for the purpose.

Insert 27 may be made of graphite, tungsten, molybdenum, tantalum, or other suitable refractory material. Graphite is shown in the embodiment herein illustrated.

The internal nozzle designated generally by numeral 15 is firmly attached to motor casing 11 lby bolts 35, extending through holes in `shoulder 24 and steel retainer ring 37. The bolts .are threaded into-a lflange 39, welded or yotherwise attached to the motor casing, whereby the nozzle shoulder is held securely thereto. f

The internal plastic nozzle of this invention has been test fired many times and proved superior to the metalgraphite and other nozzle designs 'i heretofore used.

When the heat-resistant nozzle composed of the asbestos-filled thermosetting phenolic resin or other like material is molded ldirectly into the motor shell or casin the metal retaining-.ring is no longer required.

The present 4internal plastic nozzle for -a composite propellant system may be lfabiicatedof anyheat-resistant thermosetting type resin containing a ller. The fillers are usually powders of metals, metal oxides, or ceramics,

iibers of asbestos, glass, ref-rasil and graphite. Nozzles made from formulations containing powder or nonoriented fibers .are usually molded to shape. Those made from laminates or Aoriented fibers are usually machined from a block of molded material. When oriented fibers are used, the block is machined in such `a manner that the bers are oriented -in a direction perpendicular to the flow of rocket exhaust gases. The graphite insert withstands high temperatures and nozzle-throat erosion has been held to a minimum, thereby .reducing motor malfunction.

Nozzles for rockets have undergone m'any Idesign changes as the requirements and rocket motor firing conditions become more severe. With the constant need `for reduction in weight it has been necessary to make the body of the nozzle as thin and strong las possible. The use of .copper or steel nozzles with graphite or molybdenum inserts has been highly effective with the homogeneous propellants, but has not been satisfactory with the composite propellants due to their higher-burning temperatures and erosive exhausts. The present invention utilizing a heat-stable plastic nozzle with graphite inserts has proved successful in the composite propellant system. Furthermore, the phenolic asbestos utilized in fabrication of the present invention bonds directly to the composite grain thereby permitting higher motor loading density land consequently producing higher performance rocket motors. Copper or steel nozzles used heretofore do not Abond directly to the composite grain, and they are extremely heavy since the nozzle portion which is not protected *by graphite must be extra heavy to provide a reservoir for the heat. The nozzle of the present invention has been designed to reduce the erosion and wear on the nozzle produced by hot, high veloci-ty gases.

The present heat-stable `structure comprising phenolic asbestos with insert can be press-molded directly into the aft section of the rocket motor before or after attachment (by riveting, threading, bonding, etc.) to the motor tube. The machining, .and the separate bonding step are thereby eliminated and the cost of fabrication greatly reduced. The steel retaining ring is also eliminated.

The internal plastic nozzle When used in conjunction with a foam core yor mandrel will eliminate the head closure except for a very small entry port thereby producing an ultra light weight unit.

The present internal plastic nozzle for composite propellants permits the propellant to be head-end cast :in the motor casing. If the nozzle is first provided with yan effective closure (core, mandrel disc or other type seal), the propellant can be cast and bonded directly to the phenolic-asbestos portion of the nozzle, thus increasing the loading density and greatly reducing the amount of erosion protection required at the aft end of the motor. The steel motor casing also can be made lighter by means of minor design changes, because practically no heat is transferred to the steel through the plastic nozzle during firing.

Obviously many modifications land variations of the present invention are possible in the light of the above teachings. It is therefore to be understood that within the scope of the appended claims, the invention may be practiced otherwise than as specically described.

What is claimed is:

1. In combination with a rocket motor having a combnstion chamber,

a composite propellant grain within the chamber,

a singleaport heat-stable thermosetting plastic internal nozzle having 'an inlet portion and an exit portion with innerl [and outer walls, the 'outer Walls thereof positioned adjacent to said grain and in a sealing relation thereto,

said nozzle having an insert comprising an inlet section,

a throat section, and

an exit section positioned in contiguous relation lwith i the inlet section of said plastic nozzle land in .a sealing rela-tion there-to.

2. In combination with a rocket motor having a casing anda combustion chamber,

a composite propellant charge within the chamber,

an internal nozzle having a conical passage extending therethrough, the walls of said passage composed of a heat-stable thermosetting plastic material situated adjacent said propellant charge and converging to form Ia restricted apex portion,

a `graphite insert comprising lan inlet portion,

a throat and an exit section, said insert eXit section positioned contiguous with said apex portion and in a sealing relation thereto,

said nozzle having a shoulder at its exit section seated `against the interior Wall of the rocket motor casing land secured by a steel retaining ring.

3. A rocket motor comprising a metal casing,

a composite propellant grain positioned within the casing,

an internal nozzle comprising an exit cone,

.a throat and an inlet cone;

said exit cone composed of asbestos-filled thermosetting phenolic resin material converging to form an area of restricted diameter and having inner and youter walls;

the walls of the throat and inlet cone composed of graphite which are situated in a constraining contactual relation with the restricted diameter of the exit cone;

the outer walls of said exit cone positioned in a sealing relation with the propellant grain and secured to the aft end `of said rocket motor.

4. In combination, a rocket motor comprising a metal casing,

an internal nozzle extending into said casing and secured thereto, and

a composite propellant grain positioned within the casing, said nozzle comprising `a frusto-conical exit portion vof asbestos-filled thermosetting phenolic resin material having inner #and outer walls and a frusto-conical insert portion of graphite having `an inlet,

a throat and an outlet,

said exit and insert portions each having a `frustoconical surface in face-to-face mating relation,

said outlet of the insert portion having a wall which 'a continuation of the inner wall of the exit portion, land said composite propellant grain positioned in abutment with the outer walls of said exit portion and in a bonding relation thereto.

5. In combination, a rocket motor, comprising a casing,

a composite internal perforation propellant grain positioned within said casing,

a nozzle extending into the perforation of said grain with the major portion of the nozzle disposed within said casing, said nozzle comprising lan exit portion of asbestos-filled thermosetting phenolic resin material -secured to said casing and 'a 'graphite insert throat portion secured to ysaid exit portion,

said exit portion having inner and outer Walls joined by a frusto-conioal surface therebetween,

said Iinsert portion having a truste-conical surface,

said frusto-oonical surfaces of said insert and exit portions -being in face-to-faoe mating relation, and

said lgrain positioned in abutment with said outer Wall of said exit portion.

6. In comlbin-ation, a rocket motor lcomprising a casing,

a circular ning secured to said casing lat the rear end thereof, .said ring dening `a circular opening,

a nozzle disposed within said `opening and entending into said casing, said nozzle comprising 1an exit portion of asbestos-lled thermosetting phenolic resin material and a graphite insert throat portion secured to said exit portion,

said exit portion having frusto-conic-al inner and outer wallsv joined by -a frusto-conioal surface therebetween and =a Harige extending laterally from the rear edge of the outer Wall, .said ange *being secured to said ring,

said insert portion having a -frusto-conical surface in dace-to-face mating relation with the frusto-conioal surface of said exit portion, and f 1a composite propellant grain positioned Within said casing; said grain positioned in contiguous relation with `said -ange and outer Wall.

References Cited in the file of this patent UNITED STATES PATENTS Stolfa et al Sept. 27, Ward May 20, Sanders Nov. 1, Porcher Feb. 28, Kimmel June 13, Kimmel Aug. 8, Jett Jan. 13, Alden May 8, Herzog Aug. 14, Frey Nov. 20,

FOREIGN PATENTS Germany Ian. 21, Great Britain Mar. 9, Great Britain Sept. 26, 

1. IN COMBINATION WITH A ROCKET MOTOR HAVING A COMBUSTION CHAMBER, 